In How Many Ways Can I Get Value From A Html Select Tag Without Submitting The Form? And What Are Ways That Real Websites Use For Security Purposes?

i am learning php along with mysql and so developing a e-comm site it is very exiting when i get hindered by some error but this time it just a html thing that has stopped my const

Solution 1:

onChange events are handled by javascript, PHP is finished processing before the user sees the loaded webpage.

To do what you are asking, you will want to utilize javascript/AJAX to update the page "on the fly"